Scheduled Tasks Not working

Hi All,

I have an scheduled tasks on windows server 2008 standard, Which were working fine from couple of years.

Now we are facing the issue of skipping the tasks without any error in history tab." Next Run Time " is getting updated But the "Last Run Time" is in hold.

We had tried troubleshooting following steps:

1) Firstly, Windows update was cancelled & Restarted the server (Tasks started working fine with the End Result for 2 Days then Stopped)

2)Deleted all the tasks & scheduled the tasks again then restarted (Tasks started working again with the final outcome for few days then Stopped Issue started again)

Now we are confused and searched many Forums but we didn't find the solution.

We have 7 Tasks which triggers an .EXE File. It Runs Manually & do the process.

I have seen this System Task Running always "Certificate Services Client automatically manages digital identities such as Certificates, Keys and Credentials for the users and the machine, enabling enrollment, roaming and other services" is this might be the reason..

Need the solution ASAP, I request all pro's to find me a solution.